I have heard a 2x4 laid flat works well, especially in cold weather. My birds make do without a roost or nesting box. Small flock, currently 12 birds. Flat floor with straw. They lay eggs in one corner opposite the entrance, roost in the straw in the corner nearest the entrance. In cold weather they hunker down in the straw which keeps their feet warm. In hot weather like this some will sit on an old table outside others line up on the chicken ladder. They seem happy, my egg to bird ratio rarely goes below 80%, usually 90-100%.